18 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



firm cuticle, within which is a well-marked ectosarc or cortical 

 layer, in which an appearance of longitudinal striation may be 

 observed, probably due to an internal fluting, as in Vorticella. 

 Worm-like movements can be performed by the contraction of 

 this layer. Within the ectosarc is a more fluid endosarc, and 

 there is a large nucleus at one end. There is no contractile 

 vacuole, which is not surprising when the sluggish nature and 

 consequently slow katabolism of the animal is considered. 



Monocystis undergoes encystment as a regular part of its life- 

 history, and this is usually preceded by the conjugation of two 

 individuals, which come into contact by their anterior ends, some- 

 times fuse, but in any case assume a spherical form and become 

 surrounded by a firm cyst, said to be formed from the cuticle and 

 an altered part of the underlying protoplasm. The contents 

 of the cyst now break up into a large number of spindle-shaped 

 spores (pseudonavicellse) invested in firm envelopes, and then, by 

 a process of division, eight nucleated sickle-shaped cells (falciform 

 young) are formed within each spore, a small part of the proto- 

 plasm, however, being left unused (residual core). The falciform 

 young are ultimately liberated by rupture of the cyst and the 

 spore-envelopes. They are capable of movement by alternate 

 bending and straightening, and make their way into those cells 

 (spermatospores) from which the male sex-cells of the earthworm 

 are developed, thus becoming intracellular parasites. After a 

 time they quit these cells and gradually assume the adult form. 



Another common kind of Gregarine is Gregarina (Clepsidrina) 

 folattarum, found in the intestine of the cockroach. A mature 

 individual, when young, possesses an elongated tapering body 

 (Fig. 3), divided into three regions, (a) an anterior epimerite 

 (" cap "), provided with hook-like cuticular processes, and passing 

 into (6) a protomerite, separated by a transverse septum of ecto- 

 sarc from (c) a much larger deutomerite, in which the nucleus is 

 contained. These regions are probably not distinct cells, but 

 merety parts of one cell. Sooner or later the epimerite is thrown 

 off. 



Two individuals unite, the anterior end of one being opposite 

 the posterior end of the other, and a complicated cyst is secreted, 

 consisting of a number of firm layers with an external gelatinous 

 investment. Eepeated nuclear division presumably takes place, 

 and a considerable number of barrel-shaped spores are formed 



